Host plant odour and sex pheromone are integral to mate finding in codling moth

Behaviour-modifying chemicals mediate sexual communication and host choice in insect herbivores. Sex pheromones are believed to attract insects by themselves, even though they are released into an atmosphere of plant odorants. We show for the first time that, in codling moth, feeding on apple and pear, that female pheromone is efficient for male attraction only in the presence of host plant odour. In non-host vegetation, male attraction to sex pheromone was very strongly reduced. The role of host odour in sex attraction was then substantiated by blending synthetic pheromone, codlemone, and the kairomone pear ester, a strong host plant attractant. An admixture of pear ester entirely rescued pheromone attraction in non-host vegetation. This field behavioural assay substantiates that host plant olfactory cues are integral part of sexual communication and mate recognition, which provides a mechanism for how shifts to new host plants produce new mate recognition signals.